1. Field of the Invention
This invention is related to the conventional lay and the reeled lay methods and apparatus for laying underwater pipelines and the control of the equipment for lay of pipeline.
2. Background
As the search for oil continues to move to deeper more remote areas, there have been strides in the oil industry to create multi-faceted vessels. Moreover, the oil industry direction is to equip one vessel with the ability to perform multi tasked operations pertaining to heavy lift, offshore construction, dive support, deep water pipelay and deep water umbilical cabling systems. The prior art does not disclose a multitasking apparatus or method. It is an object of the present invention to have the ability to continuously lay all types of sub sea pipelines conventionally or reeled to include but not limited to: 1) single wall concrete, 2) single wall plastic coated, 3) single wall no coat, 4) pipe-in-pipe systems coated/uncoated (referred to in this specification as "pipe" or "pipe 215").
Many studies have been done comparing conventional and reeled methods of laying sub sea pipelines. The main advantage of the conventional lay ("stock on") method is the ability to stay on location constructing a pipeline and have the individual stalks of pipe brought out to the vessel by a material barge. The advantage of the reeled method is the ability to lay long lengths of pipe during limited weather windows. In the reel method the pipe construction is done at the quay where a costly spread of tugs, boats, fuel, full compliment of personnel, etc. are not needed in the construction of the pipeline. The prior art only shows use of one of the two modes for any barge apparatus. It is an object of the present invention to change modes of operation to be job specific.
Industry utilizes two types of storage reels for reeled pipe systems, 1) Vertical Reel, 2) Horizontal Reel. Both types possess advantages and disadvantages inherent in their designs. A disadvantage of the vertical reel is that the stability of the vessel is compromised with a high center of gravity. Another disadvantage of a vertical reel is the structure weighs more than that of a horizontal reel given the same storage capacity. It is another object of the present invention to have a significantly lower center of gravity thus creating a more stable vessel.
In certain pipeline scenarios the same pipeline can change its physical parameters due to the operational requirements and water depth. Pipelines can change wall thickness, buckle arrestors, anodes, poly-coated to concrete coated, etc. Pipelay vessels of the prior art can only satisfy one operational requirement where the pipe has to be abandoned on the seabed and another vessel has to be mobilized to complete the scope of work. This abandonment and recovery process is extremely time consuming and expensive. It is another object of the present invention to have the capability to change from reel pipelay mode to conventional pipelay mode and deal with all manner of pipe without abandoning the pipeline in open water on location.
The fatigue of the pipe is a important parameter in reeled systems. Minimizing fatigue in reeled pipe systems is paramount in ultra deep laying operations. For example, in the Chickasaw design, the pipe is subjected to reverse bending during the spooling and unreeling process. The pipe always goes through one bending operation as it is plastically deformed around the hub of the reel which reverse bends the pipe. It is an additional object of the present invention to only plastically deform the pipe once to spool and unreel the pipe on/off the storage reel.
As pipelay operations continue into deeper waters, anchor systems to position the barge are limiting with excessive water depth. To operate in ultra deep waters, Dynamic Positioning Systems are utilized. In pipe lay systems of the prior art, the pipe laying operations and the positioning of the vessel are independent systems with job specific personnel operating them. The efficiency and control to lay pipe utilizing these independent systems can become impaired. It is a further object of the present invention to integrate the control of both systems described into one single unit, thus having the ability to achieve maximum efficiency and control of both systems simultaneously.
The laying of sub sea pipelines has been done using either the S-lay or J-lay method. The S-lay method dictates the pipes orientation from the deck of the vessel to the seabed is in the shape of an "S", namely S-lay. The J-lay method dictates the pipes orientation from the vessel to the seabed in the shape of a "J", namely J-lay. Both methods "S" and "J" lay have their limitations. Generally, "J" lay has limitations dependent on minimum water depth and "S" lay having limitations on maximum water depth. Other S-lay operations are limited by water depth, moreover, the excessive strain imposed by the over bend of the pipe created by the stinger overcomes the structural integrity of the pipe. It is an object of the present invention to incorporate both methods.